September 8, 1974
Ford pardons Nixon
Richard Nixon is the only President of the United States to resign. Facing "possible indictment and trial for offenses against the United States," President Gerald Ford, on September 8, 1974, granted "a full, free, and absolute pardon unto Richard Nixon for all offenses against the United States ... from January 20, 1969, through August 9, 1974."
http://www.presidency.ucsb.edu/ws/?pid=4696